DESCRIPTION The proposed study is a randomized trial to evaluate two lifestyle physical activity interventions. The lifestyle approach is based on the stages of motivational readiness model and social cognitive theory, and is designed to help sedentary adults achieve the recommended 30 minutes of at least moderate intensity physical activity each day. Previous work by the investigators has found that a lifestyle physical activity intervention delivered in a "behavioral group process" setting, resulted in increases in physical activity and improvements in clinical variables such as lipoprotein profile, blood pressure, and body composition. This application proposes a three group randomized trial to develop and test the lifestyle intervention further by decreasing the intensity and cost of face-to-face interventions. The original group meeting lifestyle approach (PRIME G - group) will be compared with an intervention that provides counseling and guidance by mail and telephone (PRIME C - Correspondent). There will also be a standard care control (PRIME SC) in which participants are given a 6-month YM/YWCA membership and a general wellness newsletter. The investigators plan to recruit and randomly assign a total of 243 men and women to the three conditions. The proposed project, PRIME, is a 24-month study, with initial 6-month intensive interventions and an 18-month maintenance and follow-up period. The primary research hypothesis is that the correspondent lifestyle intervention will be as effective in increasing physical activity and endurance fitness in initially healthy sedentary men and women as the more intensive group meeting lifestyle approach and will do so at significantly less cost.